This invention relates to the field of rope braking devices generally, and, in particular, devices for use in applications where it is desirable to force-limit a tensioned rope such as in rescue belay devices used in rope rescue operations, in industrial, commercial and film rigging, in industrial fall protection, in rope access, and in boating and sailing.
In rope rescue, a separate un-tensioned back-up, often called a belay system, is commonly used to catch a falling load in the unlikely event that any component in the primary, or mainline system should fail. As yet, there are no regulatory standards of performance for the device used to xe2x80x9ccatchxe2x80x9d the falling rescue load. In the mid-eighties, a proposal was put forth to the Province of British Columbia""s Provincial Emergency Program (PEP) by the British Columbia Council of Technical Rescue (BCCTR), who at that time provided recommendations on rope rescue matters to PEP, that a rescue belay be capable of catching a 200 kg mass representing two people, plus equipment, falling one metre on three metres of 11 mm rope, with no more than one metre additional travel distance (pre-rebound) and with no more than 15 kN of peak force. The National Fire Protection Association (NFPA) has adopted a larger 272 kg mass (600 pounds) to represent a two person load, though they have not yet specified any belay competence criteria.
The NFPA is the only standard setting body at this time which considers a two person load to be 272 kg and it is largely their standards (NFPA 1983, 1995 edition) which have led to a widespread North American use of 12.7 mm kernmantle construction ropes for use in rope rescue within the fire service and industrial rescue. Outside of North America more conventionally a rescue-sized load is considered to be about 200 kg and kernmantle rope diameters of 11 mm are common. Much of the North American, British and Australian rope rescue community has loosely agreed that a relative worst case fall of a rescue sized load is a one metre drop of that load with only three metres of rope in service. However, this has yet to put into writing as a standard. These worst-case criteria represent a mainline system failure during the critical phase of backing a load over a vertical edge, leaving the belay system to catch the falling load. Because the NFPA chose a large mass to represent a two person load and rope diameter for their standards, developing a mechanical belay device that can meet the xe2x80x9cinformalxe2x80x9d relative worst-case belay competence criteria has been difficult.
To date, the only system that has met, i.e. be xe2x80x9creliablexe2x80x9d, to the BCCTR standard is the Tandem Prusik Belay (2, 3-wrap, 8 mm nylon kernmantle cord Prusik hitches in tandem on the belay rope, connected to a load releasing hitch, which is then connected to an anchor). This technique is considered to be too cumbersome and difficult to learn by many. Until now, no mechanical belay device has proven to be reliable enough to warrant its use. While some mechanical device designs have been attempted, they have all resulted in one or more serious shortcomings. For example, they require too much human gripping ability, cut the rope, they cannot release the load post-drop, etc. Conventional mechanical rope grabs, which are usually intended for ascending a rope, or catching a single person load, have also been tried for rescue belays, but with little success.
Also, many rope grabs, designed for ascending, tend to work well in one direction only, that is, taking rope in or letting rope out, but not both. In the prior art, see for example U.S. Pat. Nos. 5,850,893, 5,054,577, 4,596,314, 5,597,052, 5,076,400, 5,975,243, 5,360,083 and 5,577,576. In rescue belaying, however, the belay device should allow for easy feed in both directions. It would also be advantageous if the belay device were bi-directional, meaning that the load could be attached to either end of the rope exiting the belay device, and it would still work. This would help reduce the risk of human error when loading the rope into the device.
Another challenge has been to find a rescue belay device that can work well for a range of rope diameters, and not be limited to just one brand of rope. Typical kernmantle construction rescue ropes, have properties (e.g. stiffness, actual vs. nominal diameter, braid technique, elongation, etc.) that vary considerably between manufacturers. Variations in rope properties exist because of differing beliefs among users and manufacturers between which properties are most important for rope rescue. Some of these properties have diametrically opposing needs. A rope-brand specific device has limited value as rope rescue groups and agencies may have little control over which brand of rope is bought, other than it must pass a certain standard, like NFPA 1983.
The device of the present invention:
a) is usable on a wide range of nylon or polyester kernmantle construction rope diameters (e.g. 10.0-11.5 mm for 200 kg mass and 11.5-13.0 mm for 280 kg mass).
b) can catch the relative worst case fall of a rescue-sized load:
i) the minimum BCCTR belay competence drop test criteria of a 2 person, 200 kg mass falling 1 m onto 3 m of 11.1 mm rope with no more than 1 m additional travel distance (pre-rebound) and no more than 15 kN peak force;
ii) similar to above but with a 280 kg mass (representing an NFPA sized load) falling 1 m onto 3 m of 12.7 mm rope, again with a target of no more than 1 m additional travel and with no more than 15 kN peak force;
c) after a fall-arrest, the load can be lowered with control by use of a manually operable release lever;
d) has bi-directional action, i.e. the load can be on either rope-end exiting the belay device thereby minimizing the risk of human error when loading the rope into the device;
e) self-locks during a shock force, and for a xe2x80x9cslowxe2x80x9d fall-like tumble, it requires some (up to 30 N) belayer, i.e. human, gripping ability to trigger fall arrest if the smallest diameter, most supple rope was used. With stiffer, large diameter ropes, even a tumble will likely trigger fall arrest;
f) works on dry, wet, muddy and icy ropes, although any solidly frozen rope will be very difficult to handle;
g) is relatively light (approximately 650 grams);
h) is easy to load the rope;
i) is durable (can withstand rough handling);
j) exceeds the NFPA 1983-1995 edition Auxiliary Equipment minimum 3-sigma static breaking strength of 36.0 kN;
k) can easily feed the rope through the device for belaying and also provides that the tension in the rope is releasable for example by manually selectable unlocking of the self-locking brake mechanism as described above.
In summary, the force limiting rope brake device of the present invention includes a pair of rigid first and second side-plates in parallel overlaid array sandwiching therebetween a pivotally mounted pulley. The pulley pivots about a pivot axis extending orthogonally between parallel first and second planes, the first and second planes containing first ends of the first and second side-plates.
The pulley is elongate, for example oval or obround, when viewed in cross-section parallel to the first and second planes. The pulley is pivotally mounted at a first end of the pulley so that the pivoting of the pulley rotates an opposite second end of the pulley in an arc between the side-plates about the pivot axis. The arc sweeps out an arcuate path parallel to the first and second planes and centered relative to the first and second side-plates.
The arcuate path is bounded at its ends by stops. The stops may engage a rigid follower, mounted to the pulley, sliding along a channel or arcuate aperture in the first side-plate. The stops constrain rotation of the pulley about the pivot axis between fully rotated first and second positions symmetrically and oppositely disposed on opposite sides of a center plane bisecting the first and second side-plates and orthogonal to the first and second planes.
A pair of rigid wedges are rigidly mounted between the first and second side-plates on opposite lateral sides of the pulley. The first and second wedges and the pulley when in the first and second positions define, respectively, first and second gaps, the first and second gaps identical in size and sized so that rope segments journalled through the first and second gaps are compressed in either the first or second gaps when the pulley is rotated into either the first or second positions respectively.
The pulley is sized to receive 1xc2xd wraps of the rope around a smooth, advantageously non-finished, rope engaging surface of the pulley parallel to the wedges. Further advantageously the wraps of rope are separated by wrap-separating means such as oppositely extending pins mounted to the rope engaging surface of the pulley. Further still, the wedges on their rope engaging surfaces, may be striated perpendicularly to the first and second planes such as by a parallel array of grooves.
The force limiting rope brake device of the present invention may also be described as including a pivotally mounted elongate pulley mounted to a base. The pulley pivots about a pivot axis extending orthogonally from the base.
The pulley is pivotally mounted at a first end of the pulley so that the pivoting of the pulley rotates an opposite second end of the pulley in an arc about the pivot axis. The arc sweeps out an arcuate path generally parallel to the base.
The arcuate path is bounded at its ends by stops. The stops may engage a rigid follower, mounted to the pulley, sliding along a channel or arcuate aperture in the first side-plate. The stops constrain rotation of the pulley about the pivot axis between fully rotated first and second positions symmetrically and oppositely disposed on opposite sides of a center plane bisecting the arc and orthogonal to the base.
A pair of rigid wedges are rigidly mounted to the base on opposite lateral sides of the pulley. The first and second wedges and the pulley when in the first and second positions define, respectively, first and second gaps, the first and second gaps identical in size and sized so that rope segments journalled through the first and second gaps are compressed in either the first or second gaps when the pulley is rotated into either the first or second positions respectively.
The pulley is sized to receive one and one half wraps of the rope around a smooth, rope engaging surface of the pulley parallel to the wedges. Further, the wraps of rope may be separated by a wrap-separating means such as oppositely extending pins mounted to the rope engaging surface of the pulley. Further still, the wedges on their rope engaging surfaces, may be striated perpendicularly to the first and second planes such as by a parallel array of grooves.
The base may have an arcuate aperture therein. A rigid follower is mounted to the pulley so as to slide in the arcuate aperture. Ends of the aperture at the ends of the arcuate path form the stops.
A cam lever may be pivotally mounted to the follower so as to dispose a cam on one end of the cam lever on an opposite side of the follower, opposite to a handle on the cam lever. The cam engages rigid members on the base upon rotation of the handle to thereby urge rotation of the pulley about the pivot axis and to thereby release the rope when clamped between one of the wedges and the pulley.
A rope retainer may be mounted to the pulley, opposite to the base, so as to retain on the pulley a rope wound onto the pulley during translation of the rope through the pulley. The base may be a first plate. The retainer may be a second plate. The first and second plates may be generally parallel and the pulley pivotally mounted so as to be sandwiched therebetween.